This invention relates to a circuit configuration for monitoring the temperature of the structural element for a semiconductor component such that temperatures exceeding a preset limit are detected.
FIG. 1 is a schematic illustration of a bipolar transistor 1 thermally coupled to the semiconductor structural element to be monitored. By way of example, the element could be a power MOSFET or a power IC.
The circuit includes a bipolar transistor 1 connected in series with a current source 2 such as an N-channel depletion transistor. A Zener diode 3 is connected in parallel with the bipolar transistor 1 to limit the collector-emitter voltage. A series connection of a MOSFET 4, a resistor 9 and a current source 5 is connected in parallel with the transistor 1 and current source 2. More specifically, the collector terminal C of the bipolar transistor 1 is connected to the source terminal S of the MOSFET 4, and the gate terminal G of MOSFET 4 is connected to the emitter terminal E of the bipolar transistor. A Zener diode 6 can be connected in parallel to the current source 5, which can also be implemented as an n-channel depletion transistor. The resistance 9 represents the ON state D.C. resistance of the MOSFET 4.
When an operating voltage V.sub.DD is applied between terminal 7 and ground, the current flowing through bipolar transistor 1 depends upon the temperature of the transistor 1. Accordingly, the current flowing through the bipolar transistor 1 also depends on the temperature of the semiconductor structural element since the transistor 1 and structural element are thermally coupled.
The bipolar transistor 1 and the current source 2 are sized such that below the critical temperature of the structural element, the current flowing through the bipolar transistor 1 is smaller than the current supplied by the current source 2. Consequently, the gate terminal G of the p-channel MOSFET 4 is negatively biased relative to the operating voltage V.sub.DD and the MOSFET 4 is conducting. The gate-source voltage of the MOSFET 4 is limited through the Zener diode 3, and the conducting MOSFET 4 draws a current whose level is determined by the ON state resistance 9 and the current supplied by the current source 5.
If the temperature of the semiconductor structural element, and hence of the bipolar transistor 1 increases, then the current through the bipolar transistor increases. If, upon reaching the critical temperature, the current through the bipolar transistor 1 becomes greater than the current through the current source 2, the current source 2 effectively has a step increase in resistance. This step increase causes the potential at the emitter of the bipolar transistor 1 increase and causes the potential at the gate terminal of the MOSFET 4 to increase to a value which is near the operating voltage. Accordingly, the MOSFET 4 is switched off and the voltage at the output terminal 8 assumes a value near ground potential. This signal can be detected as an excess temperature signal.
The zero-signal current of this circuit configuration is composed of the current flowing through the bipolar transistor 1 and that flowing through MOSFET 4. Normally, this current can be in the range of 10 uA, and this current level is undesirable for many application. For example, this current level is undesirable in the motor vehicle field.